1. Field of the Invention
The present invention relates to a zoom lens and an optical apparatus.
2. Description of the Related Art
A zoom lens applied to an optical apparatus is required for a smaller size and for corrected chromatic aberrations in a lens unit. For example, a camera can be made smaller by making smaller a zoom lens in a retractable lens barrel so as to reduce the space in the retracted state. On the other hand, there is proposed a radial gradient-index lens that can form a refractive index distribution configured to cancel the chromatic aberration, and the number of lenses can be reduced when this lens is applied.
Japanese Patent Laid-Open No. (“JP”) 09-080304 discloses an objective lens in which a variety of aberrations are well corrected with about two lenses in wide angles equal to or larger than an angle of view of 80°. JP 11-006960 discloses a lens system that includes a first lens unit having a negative refractive power and a second lens unit having a positive refractive power, wherein the second lens unit is comprised of a single radial type gradient-index lens having the positive power.
Each lens unit is configured movable in the zoom lens, and a light incident status varies. Therefore, the chromatic aberration cannot be sufficiently corrected only by applying the radial type gradient-index lens to the zoom lens. The optical system of JP 09-080304 assumes an objective lens having a fixed focal length, and does not assume the zoom lens. In the zoom lens disclosed in JP 11-006960, the radial type gradient-index lens in the second lens unit is too thick to shorten the overall length of the optical system when the zoom lens is retracted.